The present invention generally relates to anvil designs used in association with rivet setting machines, and more specifically relates to an anvil design which provides that less force is needed to install a self-piercing rivet.
Self-piercing rivets are used in a variety of applications in order to attach a component to a workpiece or two workpieces together. When a self-piercing rivet is installed to join two workpieces together, the rivet pierces a first workpiece and an anvil deforms the rivet and accommodates deformation of a second workpiece so that while the rivet head is spread to hold the workpieces together in clamped engagement, the rivet does not pierce the second workpiece and, in effect, becomes encapsulated. As a result, the two workpieces become secured together.
This process is generally performed using a rivet setting machine 20, like the one illustrated in FIGS. 1 and 2. The rivet setting machine 20 is typically hydraulically powered and has a generally C-shaped frame 22. One end of the C-shaped frame 22 has a carrier head 24 which holds the rivets 26 therein prior to their being attached to the workpieces 28, 30. Above the carrier head 24 is a driver 32 which drives the rivets 26 from the carrier head 24 into the workpieces 28, 30 along an axis 34. At the opposite end of the C-shaped frame 22, an anvil 136 is attached thereto in alignment with the carrier head. 24. The anvil 136 is used to support the workpieces 28, 30 during the riveting process and has a cavity (not shown in FIGS. 1 or 2, but see FIGS. 3 and 4) therein which allows for the accommodation of the deformation of the rivet 26 and the workpieces 28, 30 during the riveting process.
The cavity 138 in the anvil 136 illustrated in FIGS. 3-9 is representative of the configuration of a cavity that has typically been provided in anvils used in such rivet setting machines 20 for the accommodation of the deformation of the rivets 26 and the workpieces 28, 30 during a riveting process. As best illustrated in FIG. 3, the anvil 136 generally has a first portion 140 and a second portion 142. The second portion 142 is dimensioned to fit within the C-shaped frame 22 of the rivet setting machine 20 while the first portion 140 is dimensioned to rest on top of the C-shaped frame 22. At an end 144 of the first portion 140 opposite where the first portion 140 and the second portion 142 of the anvil 136 are joined together, the cavity 138 is formed therein. The end 144 of the first portion 140 also supports the workpieces 28, 30 during the riveting process.
At the end 144 of the first portion 140, the cavity 138 has a diameter that is smaller than a diameter of the first portion 140 of the anvil 136. The cavity 138 typically defines a side wall 146 that extends from the end 144 of the first portion 140 into the first portion 140 toward the second portion 142. The side wall 146 initially extends from the end 144 toward the second portion 142 at a straight, inward angle such that the diameter of the cavity 138 proximate to the end 142 is larger than the diameter of the cavity 138 proximate to the second portion 142. The side wall 146 then extends further into the first portion 140 toward the second portion 142 at an arc, such that the arced portion 148 of the side wall 146 more dramatically extends toward a center 152 of the first portion 140 than does the straight, angled portion 150 of the side wall 146.
The cavity 138 further defines a main portion 154. The main portion 154 extends from the end of the arced portion 148 of the side wall 146 toward the center 152 of the first portion 140. The main portion 154 extends from the end of the arced portion 148 toward the center 152 at a straight angle toward the end 144 of the anvil 136. Thus, the arced portion 148 of the side wall 146 is the furthest portion of the cavity 138 from the end 144 of the anvil 136.
Disadvantages have arisen with such an anvil design, which will be discussed in regard to the riveting process with such an anvil 136 being used, as illustrated in FIGS. 5-9. As illustrated in FIG. 5, the end 144 of the anvil 136 supports the workpieces 28, 30 and the rivet 26 is forced into contact with the workpiece 28 by the rivet setting machine 20, such that it begins to pierce through the workpiece 28. As the rivet 26 continues to pierce through the workpiece 28, as illustrated in FIGS. 6 and 7, the workpiece 30 deforms into the cavity 138 of the anvil 136 such that the main portion 154 of the cavity 138 supports the workpiece 30.
As illustrated in FIGS. 8 and 9, the continued forcing of the rivet 26 into the workpieces 28, 30, which is necessary for the attachment of the rivet 26 to the workpieces 28, 30, causes the workpiece 30 and the rivet 26 to deform in accordance with the configuration of the cavity 138 such that the rivet 26 is forced toward the arced portion 148 of the cavity 138, thus forcing the deformation of the workpiece 30 to abut against the main portion 154, the arced portion 148 and the side wall 146.
This forcing of the deforming of the workpiece 30 into the main portion 154, the arced portion 148 and the side wall 146 has many disadvantages. One such disadvantage is that during the riveting process, the stress is elevated as there is no place for the material of the workpiece 30 to flow to during the latter stages of the riveting process. The prior art anvil configuration also causes an extreme amount of wear and tear on the anvil 136 because of the material of the workpiece 30 being forced against the main portion 154, the arced portion 148 and the side wall 146. The prior art anvil configuration further does not allow for a wide variance in the range of material thickness of the workpieces 28, 30 that can be handled, such that it can not be ensured that the riveting process will be completed when a variety of thicknesses of workpieces are used, as a thicker workpiece may not be able to be fully deformed within the cavity 138.
Such disadvantages with the prior art anvil configuration have necessitated the need for an improved anvil configuration which overcomes these disadvantages.
A general object of an embodiment of the invention is to provide an anvil configuration for a rivet setting machine that provides a cavity with a relief pocket such that material from a workpiece can flow without encountering resistance from the sidewalls of the anvil during a riveting process.
Another object of an embodiment of the invention is to provide an anvil configuration for a rivet setting machine that allows for the reduction in power or load required for the riveting process.
Yet another object of an embodiment of the invention is to provide an anvil configuration for a rivet setting machine that allows for the downsizing of the C-frame of the rivet setting machine.
Another object of an embodiment of the invention is to provide an anvil configuration for a rivet setting machine that allows for the rivet setting machine to be a pneumatic unit as opposed to a hydraulic unit.
Still another object of an embodiment of the invention is to provide an anvil configuration that reduces the wear on the anvil during the riveting process.
Yet another object of an embodiment of the invention is to provide an anvil configuration that allows the rivet setting machine to handle a wider variance in the range of material thickness of the workpieces to be joined together.
Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides an anvil for a rivet setting machine configured to drive a rivet into a workpiece within a riveting process. The anvil has a cavity therein configured to accommodate a deformation of the rivet and the workpiece during the riveting process. The cavity is defined by a main portion configured to support the workpiece during the riveting process and a relief portion that is proximate to the main portion. The relief portion is configured to provide an area into which the workpiece and the rivet deform during the riveting process. The relief portion includes at least one relief pocket configured to maintain an area which remains unoccupied by the workpiece and the rivet throughout the entire riveting process. The relief portion does not substantially hinder the workpiece and rivet during the riveting process and allows the workpiece and rivet to freely deform during the riveting process.